The following commit has been merged into the x86/mm branch of tip:
Commit-ID: 652c5bf380ad018e15006a7f8349800245ddbbad
Gitweb: https://git.kernel.org/tip/652c5bf380ad018e15006a7f8349800245ddbbad
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Mon, 29 Aug 2022 12:18:03 +02:00
Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Thu, 01 Sep 2022 11:10:19 -07:00
x86/mm: Refuse W^X violations
x86 has STRICT_*_RWX, but not even a warning when someone violates it.
Add this warning and fully refuse the transition.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/YwySW3ROc21hN7g9@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
arch/x86/mm/pat/set_memory.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 6a9043b..1a2d637 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -580,6 +580,33 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start,
}
/*
+ * Validate and enforce strict W^X semantics.
+ */
+static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long start,
+ unsigned long pfn, unsigned long npg)
+{
+ unsigned long end;
+
+ if (!cpu_feature_enabled(X86_FEATURE_NX))
+ return new;
+
+ if (!((pgprot_val(old) ^ pgprot_val(new)) & (_PAGE_RW | _PAGE_NX)))
+ return new;
+
+ if ((pgprot_val(new) & (_PAGE_RW | _PAGE_NX)) != _PAGE_RW)
+ return new;
+
+ end = start + npg * PAGE_SIZE - 1;
+ WARN_ONCE(1, "CPA refuse W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
+ (unsigned long long)pgprot_val(old),
+ (unsigned long long)pgprot_val(new),
+ start, end, pfn);
+
+ /* refuse the transition into WX */
+ return old;
+}
+
+/*
* Lookup the page table entry for a virtual address in a specific pgd.
* Return a pointer to the entry and the level of the mapping.
*/
@@ -885,6 +912,8 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
new_prot = static_protections(req_prot, lpaddr, old_pfn, numpages,
psize, CPA_DETECT);
+ new_prot = verify_rwx(old_prot, new_prot, lpaddr, old_pfn, numpages);
+
/*
* If there is a conflict, split the large page.
*
@@ -1525,6 +1554,7 @@ repeat:
if (level == PG_LEVEL_4K) {
pte_t new_pte;
+ pgprot_t old_prot = pte_pgprot(old_pte);
pgprot_t new_prot = pte_pgprot(old_pte);
unsigned long pfn = pte_pfn(old_pte);
@@ -1536,6 +1566,8 @@ repeat:
new_prot = static_protections(new_prot, address, pfn, 1, 0,
CPA_PROTECT);
+ new_prot = verify_rwx(old_prot, new_prot, address, pfn, 1);
+
new_prot = pgprot_clear_protnone_bits(new_prot);
/*
|